Transmission mode selection for serving a user equipment in a d-mimo network

Abstract

There is provided techniques for selecting transmission mode for APs to serve a user equipment in a D-MIMO network. Information of calibration status defining whether the radio transceiver chains per each pair of the APs are mutually calibrated or not is obtained. Channel characteristics of a propagation channel between each of the APs and the user equipment are obtained. Reception capability information of the user equipment is obtained. The transmission mode for at least one subset of the APs is selected as a function of the calibration status per each pair of the APs, the channel characteristics, and the reception capability information. Instructions are provided to the subset of the APs of the selected transmission mode to be used when serving the user equipment.

1 . A method for selecting transmission mode for access points (APs) to serve a user equipment in a distributed multiple input multiple output (D-MIMO) network wherein each of the APs comprises at least one radio transceiver chain, wherein the method is performed by a centralized node in the D-MIMO network, and wherein the method comprises:
 obtaining information of calibration status defining whether the radio transceiver chains per each pair of the APs are mutually calibrated or not;   obtaining channel characteristics of a propagation channel between each of the APs and the user equipment;   obtaining reception capability information pertaining to how many data streams the user equipment is capable of simultaneously receiving;   selecting the transmission mode for at least one subset of the APs as a function of the calibration status per each pair of the APs the channel characteristics, and the reception capability information, wherein the transmission mode at least defines how the antennas of the subset of the APs are to be used for serving the user equipment; and   providing instructions to the subset of the APs of the selected transmission mode to be used when serving the user equipment   
     
     
         2 . The method according to  claim 1 , wherein selecting the transmission mode comprises:
 selecting at least one subset of the APs, wherein each subset comprises at least one of the APs, wherein, according to the calibration status, the radio transceiver chains of the APs within each subset are either mutually calibrated or not; and   assigning one of the data streams per each of the selected subsets.   
     
     
         3 . The method according to  claim 1 , wherein the radio transceiver chains per each pair of the APs are mutually calibrated when all the radio transceiver chains are phase-aligned with each other. 
     
     
         4 . The method according to  claim 1 , wherein the radio transceiver chains are phase-aligned with each other when the radio transceiver chains collectively have a phase alignment uncertainty smaller, or equal to, an uncertainty threshold value. 
     
     
         5 . The method according to  claim 4 , wherein the phase alignment uncertainty is equal to a standard deviation of a phase alignment error post calibration of the radio transceiver chains. 
     
     
         6 . The method according to  claim 4 , wherein the uncertainty threshold value is set depending on which transmission modes that are available to be selected. 
     
     
         7 . The method according to  claim 1 , wherein the channel characteristics is provided in terms of any, or any combination, of: pathloss, second-order statistics of the propagation channel, blockage, interference characteristics. 
     
     
         8 . The method according to  claim 1 , wherein, when according to the calibration status, the radio transceiver chains of the APs within each subset are mutually calibrated, the selected transmission mode involves any, or any combination, of: joint coherent beamforming from the subset of APs, diversity transmission from the subset of APs and at least one other subset of APs. 
     
     
         9 . The method according to  claim 8 , wherein the diversity transmission is of order f when there are f subsets of APs in total serving the user equipment. 
     
     
         10 . The method according to  claim 1 , wherein, when according to the calibration status, all the radio transceiver chains of the APs within each subset are not mutually calibrated, the selected transmission mode involves diversity transmission from the subset of APs. 
     
     
         11 . The method according to  claim 1 , wherein, when according to the channel characteristics, the propagation channel is detected to have a variability below a variability threshold value, the selected transmission mode involves joint coherent beamforming from the subset of APs. 
     
     
         12 . The method according to  claim 1 , wherein, when according to the channel characteristics, the propagation channel has a variability above a variability threshold value, the selected transmission mode involves diversity transmission from the subset of APs. 
     
     
         13 . The method according to  claim 10 , wherein the diversity transmission is of order f when there are f different mutually calibrated groups of radio transceiver chains within the subset of APs. 
     
     
         14 . The method according to  claim 1 , wherein the transmission mode is selected with an objective to maximize a utility metric. 
     
     
         15 . The method according to  claim 14 , wherein the utility metric pertains to any of: maximizing number of selected subset of APs, maximizing minimum signal to interference plus noise ratio for the subset of APs for serving the user equipment robustness to blocking. 
     
     
         16 . The method according to  claim 1 , wherein the method further comprises:
 selecting a transmission format for the subset of the APs as a function of the calibration status per each pair of the APs, the channel characteristics, and the reception capability information, and wherein the instructions provided to the APs comprises instructions of the selected transmission format to be used when serving the user equipment.   
     
     
         17 . The method according to  claim 16 , wherein the transmission format at least defines which modulation and coding scheme the subset of the APs is to use when serving the user equipment. 
     
     
         18 . The method according to  claim 1 , wherein the information of the calibration status comprises a calibration error estimate, and wherein the transmission format further is selected as a function of the calibration error estimate. 
     
     
         19 . A centralized node for selecting transmission mode for access points (APs) to serve a user equipment in a distributed multiple input multiple output (D-MIMO) network, wherein each of the APs comprises at least one radio transceiver chain, the centralized node comprising processing circuitry the processing circuitry being configured to cause the centralized node to:
 obtain information of calibration status defining whether the radio transceiver chains per each pair of the APs are mutually calibrated or not;   obtain channel characteristics of a propagation channel between each of the APs and the user equipment;   obtain reception capability information pertaining to how many data streams the user equipment is capable of simultaneously receiving;   select the transmission mode for at least one subset of the APs as a function of the calibration status per each pair of the APs, the channel characteristics, and the reception capability information, wherein the transmission mode at least defines how the antennas of the subset of the APs are to be used for serving the user equipment; and   provide instructions to the subset of the APs of the selected transmission mode to be used when serving the user equipment.   
     
     
         20 - 21 . (canceled) 
     
     
         22 . A non-transitory computer readable medium storing instructions for selecting transmission mode for access points (APs) to serve a user equipment in a distributed multiple input multiple output (D-MIMO) network, wherein each of the APs comprises at least one radio transceiver chain, the instructions being executable by processing circuitry of a centralized node, whereby the centralized node is caused to:
 obtain information of calibration status defining whether the radio transceiver chains per each pair of the APs are mutually calibrated or not;   obtain channel characteristics of a propagation channel between each of the APs and the user equipment;   obtain reception capability information pertaining to how many data streams the user equipment is capable of simultaneously receiving;   select the transmission mode for at least one subset of the APs as a function of the calibration status per each pair of the APs, the channel characteristics, and the reception capability information, wherein the transmission mode at least defines how the antennas of the subset of the APs are to be used for serving the user equipment; and   provide instructions to the subset of the APs of the selected transmission mode to be used when serving the user equipment.   
     
     
         23 . (canceled)